Hydrogels are three dimensional polymeric networks that can swell and retain a significant fraction, e.g., more than 20% of water within its structure, but do not dissolve. Hydrogels are well-suited for use as a base material for biologically active molecules, and have distinct advantages in these type of systems. Small molecules such as drugs can diffuse through hydrogels. Their rate of permeation can be controlled by designing the hydrogel to be specific for the intended end use. Compared to more hydrophobic materials, hydrogels have weaker interactions with molecules immobilized onto or within them. This leaves a large portion of these molecules to be active. Enzymes, for instance, when immobilized in hydrogels retain a significant fraction of their bioactivity. Hydrogels show good biocompatibility with blood and tissue, giving them an extended residence period within the tissue, making the hydrogel devices useful for long-term treatment of various conditions. Biomolecules such as enzymes can also be immobilized for later release on the large number of polar reactive sites in the hydrogel.
Biologically active molecules which may be entrapped or immobilized in hydrogels include antibiotics, drug antagonists, antibodies, estrous inducers, anticoagulants, anticancer drugs, anti-bacterial agents, enzymes, and pesticides/herbicides.
Peptic-ulcer disease (PUD) is a heterogeneous group of chronic and recurrent disorders of the alimentary mucosa, usually involving the stomach and the proximal portion of the duodenum. Gastric ulcer (GU) and duodenal ulcer (DU) are the two most common forms of PUD. The role of Helicobacter pylori in the pathogenesis of PUD has been extensively investigated. H. pylon has been strongly associated with about 80% of patients with GU and up to 100% of patients with DU. It is also associated with 85% of the patients with gastritis. H. pylon is localized in the gastric mucosa; as such, localized release of drug is desired. Certain factors govern the efficiency of the local action. For example, certain antibacterial agents, e.g., penicillin and erythromycin, are degraded by acidic pH, possibly necessitating the case of acid-stable antibiotics to avoid the chances of local drug inactivation in the stomach. Gastric residence time of locally acting agents also plays an important role. Bismuth complexes, for example, have shown better action as compared to other drugs used against H. pylon. These compounds deposit on the external surface and beneath the cell wall of the organism, not only increasing the gastric residence time but also the concentration at the site of action.